The water bed, in which the mattress is a water filled, pliant container, has gained wide acceptance. It has become a standard, readily available alternative to the spring mattress bed. The popularity of the water bed is based partly upon the fact that the water mattress, by Pascal's law, provides a more uniform supporting reaction over a wider area of the user's body. The popularity of the water filled mattress can also be attributed to the reaction offered by such a mattress to a user's movements. Upon being placed in motion, the water in a water bed is displaced such that it behaves like a resonant system comprised of a mass and spring interconnected in a low friction combination. While the oscillatory frequency of water movement depends upon the volume being moved, and while the development of standing waves in the mattress depends upon a number of variables, including the point at which input displacement of water is applied, the oscillatory frequency and the low order harmonics of that frequency are such that oscillatory motion through several cycles is experienced in response to many of the ordinary movements of the water bed user.
Not everyone wants a bed that imparts a feeling of movement. However, it is logical to assume that those who choose water beds over conventional mattresses, including very soft conventional mattresses, are looking for that kind of movement. It is also apparent that it is impossible for the water bed designer to find a design which will provide optimum results for all users. The size, and the weight, and even the number of users is unknown, and may differ from one case to another. Whatever the design in terms of length, width and thickness of the mattress, and in terms of volume of water, and the inclusion or absence of inner support structures and other variables, some user movement may be expected to produce water movement that induces a less than pleasant feeling for the user or for a bed partner. Also, in the ordinary water bed, water movement does not occur except as a reaction to user movement. That has been viewed as a deficiency, and some attempts have been made to provide more water movement by applying vibrators to the mattresses. Notwithstanding such attempts, it appears that the prior art does not include a satisfactory method or structure for imparting adequate movement to the water in a water bed in the absence of user movement.